Method for detecting CAPRIN-1 in a biological sample

ABSTRACT

This invention provides: a method for detecting a cancer, comprising measuring the expression of a polypeptide having binding reactivity through antigen-antibody reaction with an antibody against CAPRIN-1 having an amino acid sequence shown in any even-numbered SEQ ID NO shown in SEQ ID NOs: 2 to 30 in the Sequence Listing in a biological sample; a method for detecting a cancer which involves determining the presence and the amount of CAPRIN-1 in a sample of a cancer patient in order to determine the administration of a therapeutic drug targeting CAPRIN-1 to the cancer patient; and a drug and a kit for the diagnosis of a cancer, comprising an anti-CAPRIN-1 antibody.

TECHNICAL FIELD

The present invention relates to a method for detecting a cancer with CAPRIN-1 as a tumor marker.

BACKGROUND ART

Cancer is the leading cause of death. This disease is currently treated principally by surgical therapy in combination with radiation therapy and/or chemotherapy. Owing to previous advances in medical technology, cancer is now a disease highly curable by early detection, depending on its type. Therefore, there is a demand for a method for detecting a cancer which places neither physical nor economic burdens on cancer patients and can be achieved by convenient tests.

Recently, methods for assaying tumor products such as tumor markers have been widely available. The tumor products refer to, for example, tumor-related antigens, enzymes, particular proteins, metabolites, oncogenes, oncogene products, and tumor suppressor genes. Carcinoembryonic antigen CEA, glycoprotein CA19-9, prostate-specific antigen PSA, calcitonin (peptide hormone produced in the thyroid gland), and the like are exploited as tumor markers in cancer diagnosis for some cancers. For many other types of cancers, however, tumor markers useful in cancer diagnosis have not yet been found. In addition, a large majority of currently known tumor markers is present only in very small amounts (of the order of pg/mL) in body fluids and requires highly sensitive assay methods or special techniques for detecting these markers. Under such circumstances, it can be expected that doors will be opened for diagnostic use for various types of cancers if a novel cancer testing approach capable of highly sensitively detecting various types of cancers by convenient operation can be provided.

Meanwhile, in spite of recent development of novel surgical techniques or discovery of novel anticancer agents, an effective cancer diagnosis technique has not been established for many cancers, except for some cancers. Hence, these cancers cannot be detected early, and the existing cancer treatment has an insufficiently improved outcome.

With recent advances in molecular biology or cancer immunology, antibodies specifically reacting with cancer, molecular targeting drugs for cancer antigens related to malignant transformation or cancer exacerbation, and the like have been identified, raising expectations on specific cancer therapy targeting cancer antigens. Among others, a plurality of antibody drugs for cancer treatment targeting antigenic proteins on cancer cells have been launched and used in the cancer treatment. These antibody drugs have received attention because of their certain efficacy as cancer-specific therapeutic agents. A large majority of antigenic proteins targeted by the drugs, however, is also expressed in normal cells. As a result of administering the antibodies, cancer cells as well as normal cells expressing the antigens are damaged, resulting in undesired adverse reactions. In addition, the effects of cancer treatment differ very largely among individuals due to various etiologies depending on the cancer patients. For example, surgery, chemotherapy, or radiation therapy largely varies in the treatment and prognosis depending on the stages of cancers. Different persons are known to have distinctive sensitivities to the same therapeutic drug for cancers due to the diversity of individuals. Thus, a certain drug is effective for some patients but ineffective for others.

Thus, their administration to cancer patients is determined by preliminarily measuring the expression of disease-related genes or proteins in the patients and evaluating whether a particular drug is effective for a cancer patient expressing a particular gene or protein. Specifically, the presence of a cancer antigen in a sample, for example, serum or tissue, derived from a cancer patient is tested in clinical practice by use of a detection method for assaying a disease-related gene or protein of a certain kind of cancer. Then, the administration of a cancer antigen-specific therapeutic drug is determined. For example, cancer tissues from a large bowel cancer patient are evaluated by an immunohistochemical staining EGFR detection method “EGFR pharm (Dako, an Agilent Technologies Company)” to predict the effectiveness of Erbitux for the large bowel cancer. Then, the administration of Erbitux is determined. Alternatively, cancer tissues from a breast cancer patient are evaluated by an immunohistochemical staining Her2 detection method “HercepTest” to predict the effectiveness of Herceptin for the breast cancer. Then, the application of Herceptin is determined.

Incidentally, companion animals have been raised as family members and often have lifestyles similar to those of their owners. For this reason, from the occurrence of cancers in companion animals, it can reportedly be predicted that their owners have the high risk of developing cancers in the future.

Dogs which are typical companion animals are known to age 7 times more quickly than humans. Reportedly, the number of dogs currently raised is approximately 6.7 million in Japan and approximately 17.64 million in the USA. Rabies shots as well as combined vaccines such as quintuple, septuple, or octuple combination shots are generally available, leading to decreased rates of highly lethal infections including canine parvovirus infection, canine distemper infection, canine parainfluenza virus infection (kennel cough), canine adenovirus type 2 infection (kennel cough), canine infectious hepatitis, canine coronavirus infection, and leptospirosis. An average dog life-span has therefore been increased, and 7-year-old or older dogs account for 35.5% of the total number of pet dogs. The causes of death such as cancer, hypertension, and heart disease are ever increasing in dogs, as in humans. In the USA, approximately 4 million dogs are yearly diagnosed with cancers. Also in Japan, approximately 1.6 million dogs allegedly have some potential tumor. Checkup examination, however, is not very common in companion animals, unlike humans. This leads to the late detection of disease. In most cases, their owners notice pets' symptoms for the first time after tumors have already become large, and then visit animal hospitals. If such large tumors are malignant, even surgical therapy (e.g., surgical operation) or medication using anticancer agents or the like is often too late to cure the tumors. Tumors confirmed by veterinarians to be malignant are generally treated with anticancer agents without surgery. Even in the case of performing surgery, it is required to secure surgical margins or to take stringent measures for surgery such as measures against the spread of blood or cells during surgery. Desirably, treatment with anticancer agents is initiated immediately after surgery, and a follow-up is also performed at short intervals. Thus, the medication using therapeutic drugs for cancers is also essential for the cancer-affected companion animals. A detection method, if any, for assaying a disease-related gene or protein of a certain kind of cancer permits more effective treatment than ever and is advantageous both for owners and for veterinarians.

Cytoplasmic- and proliferation-associated protein 1 (CAPRIN-1) is an intracellular protein known to be expressed upon activation or cell division of resting normal cells and to form cytoplasmic stress granules with intracellular RNAs to participate in the regulation of transport and translation of mRNAs. Meanwhile, the present inventors have revealed that: CAPRIN-1 is highly expressed on the membrane surface of breast cancer cells; and an antibody against CAPRIN-1 exerts strong antitumor effects on breast cancer cells (Patent Literature 1). According to another report, the expression of CAPRIN-1 in a patient-derived sample can be measured using an antibody binding to CAPRIN-1 expressed on cell surface to thereby detect a cancer and to evaluate the grade of the cancer (Patent Literature 2). Specifically; the report states that a plasma membrane protein CAPRIN-1 may serve as a target for cancer treatment or the like. As mentioned above, due to the diversity of cancer patients, it is required to test the expression of CAPRIN-1 in a cancer patient-derived sample for determining the administration of a CAPRIN-1-targeting therapeutic drug, for example, an antibody. Nonetheless, there exists no report on a method for detecting CAPRIN-1 for the application of such a specific therapeutic drug, or there exists no reagent for detecting a cancer using a cancer patient-derived sample.

CITATION LIST Patent Literature

-   Patent Literature 1: WO2010/016526 -   Patent Literature 2: WO2010/016527

SUMMARY OF INVENTION Technical Problem

An object of the present invention is to provide a cancer detection approach useful in the diagnosis of a cancer. Another object of the present invention is to provide a method for detecting a cancer which involves detecting CAPRIN-1 in a sample of a cancer patient and determining the expression level thereof in order to determine the administration of a therapeutic drug targeting CAPRIN-1 to the cancer patient, and a drug and a kit for the diagnosis of a cancer.

Solution to Problem

As a result of conducting diligent studies, the present inventors have obtained cDNAs encoding proteins to which antibodies present in cancer-bearing organism-derived serum bind by SEREX using a dog testis-derived cDNA library and the serum of cancer-bearing dogs. Dog CAPRIN-1 having any of the amino acid sequences shown in SEQ ID NOs: 6, 8, 10, 12, and 14 was prepared on the basis of the cDNAs. The present inventors have also prepared human CAPRIN-1 having any of the amino acid sequences shown in SEQ ID NOs: 2 and 4 on the basis of human homologous genes of the obtained genes. Consequently, the present inventors have found that: genes encoding CAPRIN-1 are specifically expressed in dog and human-testis, respectively, and in malignant cancer cells (see Example 1 mentioned later); and monoclonal antibodies prepared using, as antigens, recombinant polypeptides prepared on the basis of the amino acid sequences of CAPRIN-1 can bind to CAPRIN-1 in various cancer tissues and damage cancer cells having CAPRIN-1 on their surface. As a result, the present inventors have gained the finding that CAPRIN-1 can be used as a target for cancer treatment. The present inventors have further found that CAPRIN-1 can be specifically detected from cancer patient-derived samples by use of the monoclonal antibodies mentioned above. Specifically, the present invention provides a method for detecting a cancer in a biological sample, comprising measuring the expression of CAPRIN-1. In addition, the present invention has established a method for detecting CAPRIN-1 in a cancer patient-derived sample and evaluating the expression level thereof by an immunological assay method using any of the monoclonal antibodies mentioned above, i.e., by ELISA for cancer patient-derived serum and/or an immunohistochemical staining method for cancer tissues, etc. As a result of evaluating a cancer-derived sample by use of this method, a therapeutic drug targeting CAPRIN-1 has also be found to be applicable to a patient in which CAPRIN-1 is expressed at a high level. On the basis of these findings, the present invention has been completed.

The present invention provides a method for detecting a cancer in a biological sample, comprising detecting CAPRIN-1 in the sample and measuring the expression level thereof. The present invention also provides a diagnosis method for determining the applicability of a therapeutic drug against CAPRIN-1, comprising measuring the expression level of CAPRIN-1 in a tissue before administration of the therapeutic drug against CAPRIN-1 to a cancer patient to thereby predict whether a therapeutic drug targeting CAPRIN-1, for example, an antibody, can be applied to the cancer patient and also predict the effectiveness thereof. The present invention further provides a drug or kit for the diagnosis of a cancer, comprising an antibody capable of antigen-antibody reaction with CAPRIN-1, or an antigen-binding fragment thereof.

Specifically, the present invention has the following aspects:

(1) A method for detecting a cancer, comprising measuring the expression level of CAPRIN-1 in a biological sample through antigen-antibody reaction using an antibody having immunological reactivity with a polypeptide having the amino acid sequence shown in SEQ ID NO: 63.

(2) The method for detecting a cancer according to (1), wherein CAPRIN-1 to be measured is (a) a polypeptide having an amino acid sequence shown in any even-numbered SEQ ID NO shown in SEQ ID NOs: 2 to 30 in the Sequence Listing, or (b) a polypeptide having 85% or higher sequence identity to the CAPRIN-1.

(3) The method for detecting a cancer according to (1) or (2), wherein the biological sample is derived from a human, a dog, or a cat.

(4) The method for detecting a cancer according to any of (1) to (3), wherein the biological sample is derived from a dog, and CAPRIN-1 to be measured has an amino acid sequence shown in SEQ ID NO: 6, 8, 10, 12, or 14.

(5) The method for detecting a cancer according to any of (1) to (3), wherein the biological sample is derived from a human, and CAPRIN-1 to be measured has an amino acid sequence shown in SEQ ID NO: 2 or 4.

(6) The method for detecting a cancer according to any of (1) to (5), wherein a measured CAPRIN-1 expression level which is significantly higher than that of a healthy individual indicates the presence of the cancer targeted by the antibody as a therapeutic drug for the cancer.

(7) The method for detecting a cancer according to any of (1) to (6), wherein the measurement of the expression of CAPRIN-1 employs an immunological assay method.

(8) The method for detecting a cancer according to (7), wherein the immunological assay method is ELISA and/or an immunohistochemical staining method.

(9) The method for detecting a cancer according to any of (1) to (8), wherein the sample is a body fluid, a tissue, or a cell.

(10) The method for detecting a cancer according to any of (1) to (9), wherein the cancer is at least one cancer selected from the group consisting of breast cancer, brain tumor, esophagus cancer, stomach cancer, lung cancer, liver cancer, kidney cancer, thyroid gland cancer, spleen cancer, pancreas cancer, large bowel cancer, skin cancer, ovary cancer, uterus cancer, prostate cancer, bladder cancer, testis cancer, osteosarcoma, and fibrosarcoma.

(11) The method for detecting a cancer according to any of (1) to (10), wherein the antibody or the antigen-binding fragment thereof is a monoclonal antibody having a heavy chain variable region comprising the amino acid sequence shown in SEQ ID NO: 70 and a light chain variable region comprising the amino acid sequence shown in SEQ ID NO: 71, or an antigen-binding fragment thereof.

(12) A drug or kit for the diagnosis of a cancer, comprising an antibody having immunological reactivity with a polypeptide having the amino acid sequence shown in SEQ ID NO: 63, or an antigen-binding fragment thereof.

(13) The drug or kit for the diagnosis of a cancer according to (12), wherein the antibody or the antigen-binding fragment thereof is a monoclonal antibody having a heavy chain variable region comprising the amino acid sequence shown in SEQ ID NO: 70 and a light chain variable region comprising the amino acid sequence shown in SEQ ID NO: 71, or an antigen-binding fragment thereof.

(14) A method for selecting an individual-specific therapeutic drug for a cancer, comprising: measuring the expression level of CAPRIN-1 in a biological sample using an antibody having immunological reactivity with a polypeptide having the amino acid sequence shown in SEQ ID NO: 63, or an antigen-binding fragment thereof; and, when the expression level is statistically significantly higher than that of a healthy individual, determining selecting a CAPRIN-1-targeting drug as a therapeutic drug for a cancer suitable for administration to the individual from which the biological sample is derived.

(15) The method for selecting an individual-specific therapeutic drug for a cancer according to (14), wherein the CAPRIN-1-targeting drug is an antibody having immunological reactivity with CAPRIN-1, or an antigen-binding fragment thereof.

The present specification encompasses the contents described in the specification and/or drawings of Japanese Patent Application No. 2012-160751, on which the priority of the present application is based.

Advantageous Effects of Invention

The present invention provides a novel method for detecting a cancer to measure the expression level of CAPRIN-1 in a sample separated from a cancer patient. As specifically shown in Examples mentioned later, antibodies prepared using, as antigens, recombinant polypeptides prepared on the basis of the amino acid sequence of CAPRIN-1 (also referred to as Caprin-1) specifically react with CAPRIN-1 in the serum or tissues of cancer patients. As also described later in Examples, CAPRIN-1 itself is specifically expressed at high levels in various cancer tissues. The presence and the expression level of CAPRIN-1 in a sample separated from a cancer patient can therefore be measured to thereby detect a cancer. In addition, the presence or absence of sensitivity to a CAPRIN-1-targeting drug such as an antibody drug, can be preliminarily determined to thereby select a patient to which this therapeutic drug is applicable. Specifically, the presence and the expression level of CAPRIN-1 can be preliminarily measured by the application of the present invention to a cancer patient to thereby provide more efficient treatment using an anti-CAPRIN-1 antibody.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is a diagram showing the expression patterns of a CAPRIN-1-encoding gene in normal tissues and tumor cell lines. Reference number 1 depicts the expression patterns of the gene encoding the CAPRIN-1 protein. Reference number 2 depicts the expression patterns of the GAPDH gene. The uppermost panel shows the results about dog normal tissues. The left middle panel shows the results about dog breast cancer tissues. The right middle panel shows the results about human breast cancer cell lines. The lowermost panel shows the results about various human cancer cell lines.

DESCRIPTION OF EMBODIMENTS

The method for detecting a cancer according to the present invention comprises detecting CAPRIN-1 in a biological sample and measuring the expression level thereof. The expression level of CAPRIN-1 in a sample of a cancer patient can be measured by an analysis method based on, for example, an immunological assay method using an anti-CAPRIN-1 antibody. Most of such methods are known in the art, and any of immunological assay methods using the antibody, such as immunohistochemical analysis, Western blot analysis, immunoprecipitation, molecular binding assay, ELISA, and biochemical enzyme activity assay, can be used. In this context, the “expression level” used herein includes the intracellular accumulation and abundance of the protein.

The expression of CAPRIN-1 in the sample can be differentiated by classification into scores shown in Examples. A higher score indicates that CAPRIN-1 to be measured is contained in a larger amount in the cancer tissue or cancer serum of a cancer patient. In the present invention, the term “measurement” or “assay” encompasses all of detection and qualitative, quantitative, and semiquantitative approaches.

The amino acid sequence shown in SEQ ID NO: 6, 8, 10, 12, or 14 is the amino acid sequence of dog CAPRIN-1. The dog CAPRIN-1 having this amino acid sequence has been found by SEREX using a dog testis-derived cDNA library and serum derived from cancer-bearing dogs, and identified as a polypeptide binding to an antibody specifically present in the serum derived from cancer-bearing dogs (see Example 1). CAPRIN-1 itself having the amino acid sequence shown in SEQ ID NO: 6, 8, 10, 12, or 14 can be assayed as an antigen in dog tissues by the method mentioned above to thereby diagnose the presence or absence of sensitivity of the patient to a therapeutic drug targeting CAPRIN-1 (see Examples). In this context, the phrase “having an (the) amino acid sequence” used herein means that amino acid residues are arranged in the order presented in predetermined amino acid sequence information. Thus, for example, the “polypeptide having the amino acid sequence shown in SEQ ID NO: 2” means a polypeptide of 709 amino acid residues in size in which the amino acid residues are linked in the order presented in the amino acid sequence Met Pro Ser Ala . . . (snip) . . . Gln Gln Val Asn as shown in SEQ. ID NO: 2. In the present specification, the “polypeptide having the amino acid sequence shown in SEQ ID NO: 2” is abbreviated to the “polypeptide shown in SEQ ID NO: 2”. The same holds true for the phrase “having a (the) nucleotide sequence”. In this case, the term “having” may be used interchangeably with the term “comprising” or “consisting of”.

The “polypeptide” used herein refers to a molecule that is formed through the peptide bonds of a plurality of amino acids, and encompasses not only a polypeptide molecule constituted by a large number of amino acids but a low-molecular-weight molecule having a small number of amino acids (oligopeptide) and a full-length protein. The polypeptide according to the present invention also encompasses the full-length protein of CAPRIN-1 having an amino acid sequence represented by any even-numbered SEQ ID NO shown in SEQ ID NOs: 2 to 30.

In the method of the present invention, additional mammalian CAPRIN-1 other than the dog CAPRIN-1 shown in SEQ ID NO: 6, 8, 10, 12, or 14 can also be used as an analyte. In the present specification, such non-dog mammalian CAPRIN-1 is also referred to as a “homolog” of dog CAPRIN-1. The term “CAPRIN-1” encompasses CAPRIN-1 derived from not only dogs but other mammals. Examples of the additional mammalian CAPRIN-1 that may be used as an analyte in the method of the present invention include, but not limited to, human CAPRIN-1 and cat CAPRIN-1. As specifically described below in Examples, mRNA encoding human CAPRIN-1 is significantly expressed at high levels in human testis and cancer cells, as with the dog CAPRIN-1 shown in SEQ ID NO: 6, 8, 10, 12, or 14. An anti-human CAPRIN-1 antibody, however, is not detected in the bodies of healthy humans. An anti-cat CAPRIN-1 antibody is not detected in the bodies of healthy cats, but is detected only in cancer-bearing cats. Thus, the applicability of a therapeutic drug targeting CAPRIN-1 to a non-dog mammal can also be determined by the measurement of the expression level of CAPRIN-1 derived from the non-dog mammal.

The nucleotide sequence encoding human CAPRIN-1 and the amino acid sequence thereof are as shown in SEQ ID NO: 1 and 3 and SEQ ID NO: 2 and 4, respectively, in the Sequence Listing. The sequence identity of human CAPRIN-1 to dog CAPRIN-1 is 94% for the nucleotide sequence and 98% for the amino acid sequence. Since the amino acid sequence of CAPRIN-1 is as very high as 98% even between dogs and humans, which are the genetically distantly related mammals, the amino acid sequence of CAPRIN-1 probably has high (approximately 85% or higher) sequence between non-human mammalian CAPRIN-1 and the dog CAPRIN-1. In the method of the present invention, the CAPRIN-1 whose expression level is to be measured is not particularly limited and is one having preferably 85% or higher, more preferably 95% or higher sequence identity to the amino acid sequence of the dog CAPRIN-1 shown in SEQ ID NO: 6, 8, 10, 12, or 14.

An antigenic substance, such as a protein, which has a complicated structure with a large molecular weight, usually contains a plurality of epitopes differing in structure on its molecule. Thus, plural types of antibodies that respectively recognize and bind to a plurality of epitopes on such an antigenic substance are produced in vivo. In other words, antibodies produced in vivo against the antigenic substance (e.g., protein) are polyclonal antibodies, which are mixtures of plural types of antibodies. The antibodies found by the present inventors to be specifically present in serum derived from cancer-affected organisms and to specifically bind to recombinant CAPRIN-1 through antigen-antibody reaction are also polyclonal antibodies. The term “polyclonal antibody” used in the present invention refers to an antibody that is found in serum derived from an organism containing an antigenic substance in the body, and has been induced in the organism against the antigenic substance.

Specific examples of a preferred polypeptide for use as an antigen include polypeptides of even-numbered SEQ ID NOs of SEQ ID NOs: 2 to 30 and fragments thereof.

The nucleotide sequences of polynucleotides encoding polypeptides consisting of the amino acid sequences shown in even-numbered SEQ ID NOs of SEQ ID NOs: 2 to 30 (i.e., SEQ ID NOs: 2, 4, 6, . . . 28, and 30) are shown in odd-numbered SEQ ID NOs of SEQ ID NOs: 1 to 29 (i.e., SEQ ID NOs: 1, 3, 5, . . . 27, and 29), respectively.

It is widely known to those skilled in the art that even a protein derived from a protein antigen by the substitution, deletion, addition, or insertion of a small number of amino acid residues in the amino acid sequence constituting the protein may generally have almost the same antigenicity as that of the original protein. Thus, a polypeptide having a sequence derived from the amino acid sequence of CAPRIN-1 by the substitution, deletion, addition and/or insertion of a small number of (preferably 1 or several) amino acid residues can also be used in the detection of the cancer, as with the polypeptides consisting of the amino acid sequences shown in even-numbered SEQ ID NOs of SEQ ID NOs: 2 to 30 above, as long as the polypeptide has 80% or higher or 85% or higher, preferably 90% or higher, more preferably 95% or higher, further preferably 98% or higher sequence identity to the original sequence and specifically binds to a polyclonal antibody against CAPRIN-1 through antigen-antibody reaction (hereinafter, this polypeptide is also referred to as a “specifically-reactive modified polypeptide” for the sake of convenience). Preferably, the specifically-reactive modified polypeptide has an amino acid sequence derived from the amino acid sequence of CAPRIN-1 by the substitution, deletion, addition, and/or insertion of 1 or several amino acid residues. The term “several” used herein refers to an integer of 2 to 10, preferably an integer of 2 to 6, more preferably an integer of 2 to 4.

The “sequence identity” used herein for the amino acid sequence refers to the percentage of a value determined by dividing the number of identical amino acid residues by the total number of amino acid residues in the best-matching alignments of the amino acid residues in two amino acid sequences to be compared. For the alignments, if necessary, one or both of these two sequences to be compared can be gapped. Such sequence alignments can be carried out using a well-known program, for example, BLAST, FASTA, or CLUSTAL W (Karlin and Altschul, Proc. Natl. Acad. Sci. U.S.A., 87: 2264-2268, 1993; and Altschul et al., Nucleic Acids Res., 25: 3389-3402, 1997).

Twenty types of amino acids constituting a natural protein can be divided according to similar properties into the following groups: neutral amino acids having a low polar side chain (Gly, Ile, Val, Leu, Ala, Met, and Pro); neutral amino acids having a hydrophilic side chain (Asn, Gln, Thr, Ser, Tyr, and Cys); acidic amino acids (Asp and Glu); basic amino acids (Arg, Lys, and His); and aromatic amino acids (Phe, Tyr, Trp, and His). It is known that substitution within each of these groups, i.e., conservative substitution, does not change the properties of the polypeptide in most cases. Thus, in the case of substituting the amino acid residues of CAPRIN-1, a member in each of these groups can be substituted by another member in the same group so that the binding activity against the appropriate antibody is likely to be maintained. In the present invention, however, the modified form may have non-conservative substitution as long as the modified form is provided with immunity-inducing activity equivalent to or substantially equivalent to that of the unmodified form.

The polypeptide used in the present invention can be synthesized according to chemical synthesis methods, for example, Fmoc (fluorenylmethyloxycarbonyl) and tBoc (t-butyloxycarbonyl) methods (Seikagaku Jikken Koza (Biochemical Experimentation Course in English) 1, the Japanese Biochemical Society ed., Protein Chemistry IV, Chemical Modification and Peptide Synthesis, Tokyo Kagaku Dojin Co., Ltd. (Japan), 1981). Also, the polypeptide can be synthesized by routine methods using various commercially available peptide synthesizers. Alternatively, the polypeptide can be easily prepared using genetic engineering approaches known in the art (Sambrook et al., Molecular Cloning, the 2nd edition, Current Protocols in Molecular Biology (1989), Cold Spring Harbor Laboratory Press; Ausubel et al., Short Protocols in Molecular Biology, the 3rd edition, A compendium of Methods from Current Protocols in Molecular Biology (1995), John Wiley & Sons; etc.). For example, RNA is extracted from a tissue expressing a gene encoding the human CAPRIN-1 shown in SEQ ID NO: 2 or a homologous factor thereof. From this RNA, cDNA of the gene is prepared by RT-PCR. The full-length cDNA or a desired partial fragment thereof is incorporated into expression vectors, which can then be transferred to host cells to obtain the polypeptide of interest. The nucleotide sequences of cDNAs encoding the dog CAPRIN-1 proteins shown in SEQ ID NOs: 6, 8, 10, 12, and 14 are shown in SEQ ID NOs: 5, 7, 9, 11, and 13, respectively. The nucleotide sequences of cDNAs encoding the human CAPRIN-1 proteins shown in SEQ ID NOs: 2 and 4 as human homologous factors thereof are shown in SEQ ID NOs: 1 and 3, respectively. Primers for use in RT-PCR can therefore be easily designed with reference to these nucleotide sequences. As mentioned later, a gene encoding non-human mammalian CAPRIN-1 can be amplified with primers designed with reference to the nucleotide sequence shown in any odd-numbered SEQ ID NO of SEQ ID NOs: 5 to 29. Thus, cDNA encoding, for example, cat CAPRIN-1, can also be easily prepared by the same approach as above. The RNA extraction, RT-PCR, the incorporation of cDNA into vectors, and the transfer of the vectors to host cells can be carried out, for example, by well-known methods as described below. Also, the vectors or host cells used are well known, and various products are commercially available.

The host cells may be any cell capable of expressing the above polypeptide. Examples of prokaryotic cells include E. coli. Examples of eukaryotic cells include: cultured mammalian cells such as monkey kidney cells COS1, Chinese hamster ovary cells CHO, a human embryonic kidney cell line HEK293, and mouse embryonic skin cell line NIH3T3; and budding yeast, fission yeast cells, silkworm cells, and Xenopus egg cells.

In the case of using prokaryotic cells as the host cells, the expression vectors used have an origin that permits replication in the prokaryotic cells, a promoter, a ribosomal binding site, a multicloning site, a terminator, a drug resistance gene, an auxotrophic complementary gene, etc. Examples of expression vectors for E. coli can include pUC series, pBluescript II, pET expression systems, and pGEX expression systems. DNA encoding the above polypeptide can be incorporated into such expression vectors, with which prokaryotic host cells are then transformed, followed by the culture of the obtained transformants so that the polypeptide encoded by the DNA is expressed in the prokaryotic host cells. In this respect, the polypeptide may be expressed as a fusion protein with an additional protein. In this context, the DNA encoding the above polypeptide can be obtained, for example, by the preparation of cDNA by RT-PCR as mentioned above. Alternatively, the DNA may be synthesized by routine methods using commercially available nucleic acid synthesizers as mentioned later. The nucleotide sequences of cDNAs of genes encoding the CAPRIN-1 proteins shown in SEQ ID NOs: 2 and 4 are shown in SEQ ID NOs: 1 and 3, respectively, in the Sequence Listing.

In the case of using eukaryotic cells as the host cells, expression vectors for eukaryotic cells having a promoter, a splicing region, a poly(A) addition site, etc. are used as the expression vectors. Examples of such expression vectors can include pKA1, pCDM8, pSVK3, pMSG, pSVL, pBK-CMV, pBK-RSV, EBV vector, pRS, pcDNA3, and pYES2 vectors. In the same way as above, the DNA encoding the above polypeptide used in the present invention can be incorporated into such expression vectors, with which eukaryotic host cells are then transformed, followed by the culture of the obtained transformants so that the polypeptide encoded by the DNA is expressed in the eukaryotic host cells. In the case of using expression vectors such as pIND/V5-His, pFLAG-CMV-2, pEGFP-N1, or pEGFP-C1, the polypeptide may be expressed as various fusion proteins tagged with His tag (e.g., (His)₆ to (His)₁₀), FLAG tag, myc tag, HA tag, GFP, or the like.

The expression vectors can be transferred to the host cells using well-known methods such as electroporation, a calcium phosphate method, a liposome method, a DEAE dextran method, microinjection, viral infection, lipofection, and binding with cell-penetrating peptides.

The polypeptide of interest can be isolated and purified from the host cells by a combination of separation operations known in the art. Examples thereof include treatment with a denaturant (e.g., urea) or a surfactant, ultrasonication, enzymatic digestion, salting-out, solvent fractionation and precipitation, dialysis, centrifugation, ultrafiltration, gel filtration, SDS-PAGE, isoelectric focusing electrophoresis, ion-exchange chromatography, hydrophobic chromatography, affinity chromatography, and reverse-phase chromatography.

The polypeptides obtained by these methods also include their forms of fusion proteins with other arbitrary proteins. Examples thereof can include fusion proteins with glutathione-S-transferase (GST) or His tag. The polypeptides expressed in transformed cells may undergo various intracellular modifications after translation. Such posttranslationally modified polypeptides may be used as long as these polypeptides have binding activity against the polyclonal antibody against CAPRIN-1. Examples of such posttranslational modifications can include N-terminal methionine elimination, N-terminal acetylation, glycosylation, intracellular protease-mediated limited degradation, myristoylation, isoprenylation, and phosphorylation.

In the method of the present invention, CAPRIN-1 that may be contained in the biological sample is assayed. As mentioned above, cancer cells have been found to have a significantly high expression level of CAPRIN-1 as an antigen. As specifically described below in Examples, CAPRIN-1 itself can be assayed in cancer cells or cancer tissues to thereby determine the applicability of a therapeutic drug targeting CAPRIN-1 to the patient having a high expression level of CAPRIN-1.

The polypeptide in the sample can be easily assayed by a well-known immunological assay method. Specifically, CAPRIN-1 that may be present in the sample can be assayed by immunoassay using, for example, a prepared antibody capable of antigen-antibody reaction with CAPRIN-1 or a prepared antigen-binding fragment thereof. Not only the dog CAPRIN-1 shown in SEQ ID NO: 6 but its homologous factors in other mammals, for example, human CAPRIN-1 shown in SEQ ID NO: 2 or 4 or cat CAPRIN-1, can be assayed using an antibody capable of antigen-antibody reaction with, for example, the dog CAPRIN-1 shown in SEQ ID NO: 6, or an antigen-binding fragment thereof, because the antibody has cross-reactivity.

Such an immunoassay method itself is a well-known routine method, as mentioned above. The antibody that recognizes CAPRIN-1 may be immunohistochemically tested for its reactivity with CAPRIN-1 by a method well known to those skilled in the art using a paraformaldehyde- or acetone-fixed frozen section or paraformaldehyde-fixed paraffin-embedded section of a tissue obtained from a patient during surgical operation or from an animal carrying a xenograft tissue inoculated with a cell line expressing CAPRIN-1 either spontaneously or after transfection.

The expression level of CAPRIN-1 in the sample thus immunohistochemically stained can be quantitatively determined by numerical scoring reflecting staining patterns. Two or more scores are preferably set. In the most preferred aspect, the staining patterns are classified into 4 scores. For example, CAPRIN-1 expressed on the surface of cancer cells is stained by a usual immunohistochemical staining method, and the amount thereof is given any of 4 scores reflecting its staining pattern. In such a case, each score is set as follows:

Score 0 (without CAPRIN-1 overexpression): Positive staining of the cell membrane is not observed or is observed in less than 10% of the cancer cells.

Score 1 (without CAPRIN-1 overexpression): Faint, almost unperceivable staining of the cell membrane is observed in 10% or more of the cancer cells, and these cancer cells are partially stained only at their cell membranes.

Score 2 (with CAPRIN-1 overexpression): Weak to moderate complete positive staining of the cell membrane is observed in 10% or more of the cancer cells, or strong complete positive staining of the cell membrane is observed in 10% or more and 30% or less of the cancer cells.

Score 3 (with CAPRIN-1 overexpression): Strong complete positive staining of the cell membrane is observed in 30% or more of the cancer cells.

Such a score system is specified by American Society of Clinical Oncology (USA) and approved by The Japanese Society of Pathology (Japan). A similar scoring system is also exploited in “HercepTest” for quantitatively determining the abundance of a cancer antigen Her2 in samples of patients. The quantification of Her2 is specified by the ASCO/CAP Her2 testing guidelines. In Japan, a guideline for Her2 testing including this scoring system is also specified by the pathological committee for trastuzumab.

The ratio of stained cancer cells after immunohistochemical staining described in each score can be determined by: counting at least 500 cells in the field of view using a light microscope with sensitivity increased to 4 times, 10 times, or 20 times; measuring cells that exhibit stain images of their cell membranes as described in each score; and making a trial calculation according to the following expression: The number of positive cells/The total number of cells(approximately 500 cells)×100

For the immunohistochemical staining, the antibody having reactivity with CAPRIN-1 can be stained by various methods. For example, the antibody can be visualized through reaction with a horseradish peroxidase-conjugated goat anti-mouse antibody or goat anti-chicken antibody.

The antibody capable of antigen-antibody reaction with CAPRIN-1 or an antigen-binding fragment thereof for use in the immunoassay of CAPRIN-1 itself can also be provided as a drug or kit for the diagnosis of a cancer. In this case, the drug or kit for the diagnosis of a cancer may also consist of the antibody or the antigen-binding fragment or may further comprise, for example, various additives useful in the stabilization or the like of the antibody or the antigen-binding fragment. The antibody or the antigen-binding fragment may be conjugated with a metal such as manganese or iron. Such a metal-conjugated antibody or antigen-binding fragment, when administered to the body, accumulates to a site containing the antigenic protein. Accordingly, the presence of cancer cells producing the antigenic protein can be detected by the MRI measurement or the like of the metal.

CAPRIN-1 has been found to be a plasma membrane protein that is expressed on the surface of cancer cells. Since the bodies of cancer patients contain many proteolytic enzymes, the extracellular region in the CAPRIN-1 sequence on cancer cells is separated from the cancer cells upon degradation. The extracellular region thus separated is therefore present in larger amounts in blood, compared with the intracellular region in the CAPRIN-1 sequence on the cancer cells. Accordingly, CAPRIN-1 present not only in cancer tissues fixed on slide glass but in the serum of cancer patients can be detected by the assay according to the present invention using an anti-CAPRIN-1 antibody or an antigen-binding fragment thereof capable of binding more strongly to the extracellular region of CAPRIN-1. In addition, this detection method, which employs such an antibody binding to the extracellular region of CAPRIN-1, is capable of accurately identifying a cancer patient that can be expected to get therapeutic effects by the administration of a therapeutic drug targeting CAPRIN-1, particularly, an anti-CAPRIN-1 antibody drug, and can thus provide more effective cancer treatment. Thus, in the present invention, an antibody binding to the extracellular region of CAPRIN-1 on cancer cells is preferably used. Examples of the partial peptide of the CAPRIN-1 protein containing an epitope recognized by such an antibody include peptides corresponding to extracellular regions in the amino acid sequences shown in even-numbered SEQ ID NOs of SEQ ID NOs: 2 to 30 in the Sequence Listing except for SEQ ID NOs: 6 and 18. Specific examples thereof include peptides comprising a sequence of 7 or more consecutive amino acids in the region of amino acid residues 50 to 98 or amino acid residues 233 to 344 in SEQ ID NO: 2, and peptides comprising a sequence of 7 or more consecutive amino acids in a region homologous to these amino acid residues in an amino acid sequence shown in any even-numbered SEQ ID NO of SEQ ID NOs: 4 to 30 except for SEQ ID NOs: 6 and 18. More specific examples thereof include the amino acid sequence shown in SEQ ID NO: 43 or 61, preferably the amino acid sequence shown in SEQ ID NO: 62 in the amino acid sequence shown in SEQ ID NO: 61, and amino acid sequences having 80% or higher, preferably 85% or higher, more preferably 90% or higher, further preferably 95% or higher sequence identity to the amino acid sequence. The antibody used in the present invention encompasses all of antibodies binding to any of these peptides. Specific examples thereof include antibodies binding to the amino acid sequence shown in SEQ ID NO: 63 or antigen-binding fragments thereof, and monoclonal antibodies or antigen-binding fragments having the amino acid sequence of a monoclonal antibody having the amino acid sequences shown in SEQ ID NOs: 70 and 71 or an antigen-binding fragment thereof.

The “antigen-binding fragment” used herein means any antibody fragment having the ability to bind to the antigen, such as a Fab or F(ab′)2 fragment contained in an antibody molecule. The antibody may be a polyclonal antibody or may be a monoclonal antibody. A highly reproducible monoclonal antibody is preferred for immunoassay or the like. These polyclonal and monoclonal antibodies can be prepared by a well-known method using a peptide as an immunogen and can be easily obtained by a routine method. The immunization method involves immunizing the animal with, for example, CAPRIN-1 conjugated with a carrier protein such as keyhole limpet hemocyanin (KLH), casein, or serum albumin as an immunogen together with an adjuvant to thereby induce an antibody against CAPRIN-1. The antibody-producing cells (e.g., spleen cells or lymphocytes) collected from the immunized animal are fused with myeloma cells to prepare hybridomas. Then, hybridomas producing antibodies binding to CAPRIN-1 are selected and proliferated. Monoclonal antibodies adaptable to CAPRIN-1 as an antigen can be obtained from the culture supernatant. This method is a well-known routine method.

The cancer to be detected by the method of the present invention is a cancer overexpressing CAPRIN-1. Examples thereof include breast cancer, brain tumor, esophagus cancer, stomach cancer, lung cancer, liver cancer, kidney cancer, thyroid gland cancer, spleen cancer, pancreas cancer, large bowel cancer, skin cancer, ovary cancer, uterus cancer (uterine cervix cancer and uterine body cancer), prostate cancer, bladder cancer, testis cancer, and osteosarcoma. Other examples thereof can include, but not limited to, squamous cell cancer of the head and neck, melanoma, various types of adenocarcinomas, hepatocellular cancer, basal cell cancer, acanthoma-like gingival tumor, tumor mass in the oral cavity, perianal gland cancer, tumor mass of the anal sac, anal sac apocrine adenocarcinoma, Sertoli cell carcinoma, vaginal vestibule cancer, sebaceous cancer, sebaceous epithelioma, sebaceous adenoma, sweat gland cancer, adenocarcinoma in the nasal cavity, adenocarcinoma of the nose, bronchial adenocarcinoma, ducal cancer, mammary gland cancer, mammary complex carcinoma, malignant mixed tumor of the mammary gland, intraductal papillary adenocarcinoma, fibrosarcoma, hemangiopericytoma, chondrosarcoma, soft tissue sarcoma, histiocytic sarcoma, myxosarcoma, primitive sarcoma, mastocytoma, cutaneous leiomyoma, intraperitoneal leiomyoma, leiomyoma, lymphoma, chronic lymphocytic leukemia, gastrointestinal lymphoma, lymphoma of the digestive organ, small/medium cell lymphoma, adrenal medullary tumor, granulosa cell tumor, and pheochromocytoma.

The biological sample to which the method of the present invention is applied is derived from a mammal and preferably from a human, a dog, or a cat.

Examples of the sample that is subjected to the method of the present invention include body fluids, tissues, and cells. The “body fluid” used herein refers to a biological sample in a liquid state. Examples thereof include blood (including serum, plasma, and interstitial fluid), lymph, ascites, pleural effusion, spinal fluid, sputum, lacrimal fluid, nasal discharge, saliva, urine, vaginal fluid, and semen. The body fluid may include, for example, peritoneal washings with saline. Serum, plasma, ascites, or pleural effusion is preferred.

In the method of the present invention, when the measured CAPRIN-1 expression level in the biological sample is higher (preferably, statistically significantly higher) than that of a healthy individual, the presence of a cancer that can be specifically bound by the anti-CAPRIN-1 antibody used in the measurement (i.e., a cancer that can be targeted by the antibody as a therapeutic drug for the cancer) is determined in the organism (individual) from which the biological sample is derived. By use of this, the expression level of CAPRIN-1 in a cancer patient-derived biological sample can be measured by the method of the present invention and compared with that of a healthy individual to confirm whether or not a therapeutic drug against CAPRIN-1 is applicable to the cancer in the patient (e.g., whether or not the cancer in the patient can be targeted by the antibody as a therapeutic drug for the cancer).

Thus, the method of the present invention can identify a cancer patient that can be expected to get therapeutic effects by the administration of a therapeutic drug including a CAPRIN-1-targeting antibody, and thus provide more effective cancer treatment.

According to one embodiment, the present invention relates to a method for selecting an individual-specific therapeutic drug for a cancer, comprising: measuring the expression level of CAPRIN-1 in a biological sample using an antibody having immunological reactivity with a polypeptide having the amino acid sequence shown in SEQ ID NO: 63; and, when the expression level is higher (preferably, statistically significantly higher) than that of a healthy individual, selecting a CAPRIN-1-targeting drug, preferably an antibody having immunological reactivity with CAPRIN-1 or an antigen-binding fragment thereof, as a CAPRIN-1-targeting therapeutic drug for a cancer suitable for administration to the individual from which the biological sample is derived. This selection of the individual-specific therapeutic drug for a cancer realizes so-called tailor-made medicine, which offers cancer therapy optimized for an individual patient.

The term “statistically significantly” used herein means that statistically treated quantitative difference between the two is a significant difference. Specifically, examples thereof include the case where a significance level is smaller than 5%, 1%, or 0.1%. The method of verification is not particularly limited as long as the method is known in the art and is capable of determining the presence or absence of significance. For example, a Student's t test or multiple comparison test method can be used.

EXAMPLES

Hereinafter, the present invention will be described more specifically with reference to Examples. However, the scope of the present invention is not intended to be limited by these Examples.

Example 1 Analysis of CAPRIN-1 Expression in Each Tissue

The expression of the CAPRIN-1 gene in dog and human normal tissues and various cancer tissues or cancer cell lines was examined by RT-PCR according to Example 1(4) of WO2010/016526. The result is shown in FIG. 1. As a result, its strong expression was observed in the testis among the normal tissues of the healthy dog. Also, the expression was observed in dog breast cancer. Further, the expression of the gene was also confirmed using human tissues. As a result, the expression was confirmed only in the testis among the normal tissues, as with the dog CAPRIN-1 gene, but was detected in many types of cancer cell lines such as 8 human breast cancer cell lines (ZR75-1, MCF7, T47D, SK-BR-3, MDA-MB-157, BT-20, MDA-MB-231V, and MRK-nu-1) as well as 4 brain tumor cell line, 3 leukemia-derived cell line, 1 lung cancer cell line, and 2 esophagus cancer cell line. These results demonstrated that CAPRIN-1 is not expressed in normal tissues except for the testis, but is expressed in many cancer cells including breast cancer cells.

Example 2 Preparation of Anti-CAPRIN-1 Antibody

(1) Preparation of Mouse Anti-human CAPRIN-1 Monoclonal Antibody

100 μg of human CAPRIN-1 having the amino acid sequence shown in SEQ ID NO: 2 as prepared in Example 3 of WO2010/016526 was mixed with an equal amount of MPL+TDM adjuvant (Sigma-Aldrich Corp.). This mixture was used as an antigen solution per mouse. Said antigen solution was intraperitoneally administered to each 6-week-old Balb/c mouse (Japan SLC, Inc.). Then, 3 boosters were performed every 1 week. Three days after the final shot, the spleen of the mouse was excised and ground between two sterilized glass slides. Procedures of washing with PBS(−) (Nissui Pharmaceutical Co., Ltd.) and removing the supernatant by centrifugation at 1500 rpm for 10 minutes were repeated three times to obtain spleen cells. The obtained spleen cells were mixed with mouse myeloma cells SP2/0 (purchased from ATCC) at a ratio of 10:1. 200 μL of an RPMI1640 medium containing 10% FBS was heated to 37° C. and mixed with 800 μL of PEG1500 (Boehringer Ingelheim GmbH), and the PEG solution thus prepared was added to the cell mixture, which was then left standing for 5 minutes for cell fusion. After removal of the supernatant by centrifugation at 1700 rpm for 5 minutes, the cells were suspended in 150 mL of an RPMI1640 medium containing 15% FBS supplemented with 2% equivalent of a HAT solution (Gibco) (HAT selective medium). This suspension was inoculated to fifteen 96-well plates (Nunc) at 100 μL/well. The spleen cells and the myeloma cells were fused by culture under conditions at 37° C. for 7 days in 5% CO₂ to obtain hybridomas.

The prepared hybridomas were screened with the binding affinity of antibodies produced by the hybridomas against CAPRIN-1 as an indicator. The 1 μg/mL CAPRIN-1 solution was added to a 96-well plate at 100 μL/well and left standing at 4° C. for 18 hours. Each well was washed three times with PBS-T. Then, a 0.5% bovine serum albumin (BSA) solution (Sigma-Aldrich Corp.) was added thereto at 400 μL/well and left standing at room temperature for 3 hours. The solution in each well was discarded, and each well was washed three times with 400 μL of PBS-T. Then, the culture supernatant of each hybridoma obtained above was added thereto at 100 μL/well and left standing at room temperature for 2 hours. Each well was washed three times with PBS-T. Then, HRP-labeled anti-mouse IgG (H+L) antibodies (Life Technologies, Inc.) diluted 5000-fold with PBS were added thereto at 100 μL/well and left standing at room temperature for 1 hour. Each well was washed three times with PBS-T. Then, a TMB substrate solution (Thermo Fisher Scientific Inc.) was added thereto at 100 μL/well and left standing for 15 to 30 minutes to cause color reaction. After the color development, the reaction was terminated by the addition of 1 N sulfuric acid at 100 μL/well. The absorbance was measured at 450 nm and 595 nm using an absorption spectrometer. As a result, several hybridomas producing antibodies having high absorbance were selected as candidate lines of the hybridoma of interest.

The selected hybridomas were added to a 96-well plate at a density of 0.5 cells/well and cultured in the plate. One week later, hybridomas forming single colonies in the wells were observed. The cells in these wells were further cultured, and the cloned hybridomas were screened in the same way as above with the binding affinity of antibodies produced by the hybridomas against CAPRIN-1 as an indicator. A plurality of hybridoma lines producing monoclonal antibodies reactive with CAPRIN-1 protein was obtained. The culture supernatants of these hybridomas were purified using a protein G carrier to obtain 150 monoclonal antibodies binding to CAPRIN-1.

Next, monoclonal antibodies above were screened for antibodies reactive with the surface of breast cancer cells expressing CAPRIN-1. Specifically, 10⁶ cells of a human breast cancer cell line MDA-MB-231V were centrifuged in a 1.5-mL microcentrifuge tube. 100 μL of the supernatant of each hybridoma obtained above was added thereto and left standing for 1 hour on ice. After washing with PBS, FITC-labeled goat anti-mouse IgG antibodies (Invitrogen) diluted 500-fold with PBS containing 0.1% fetal bovine serum were added thereto and left standing for 1 hour on ice. After washing with PBS, the fluorescence intensity was measured using FACSCalibur (Becton, Dickinson and Company). On the other hand, the same operation as above was performed by the addition of a medium instead of the antibodies to prepare a control. As a result, 10 monoclonal antibodies (#1 to #10) having stronger fluorescence intensity than that of the control, i.e., reactive with the surface of breast cancer cells, were selected. The respective amino sequences of the heavy chain and light chain variable regions of these monoclonal antibodies are shown in SEQ ID NOs: 44 to 60. The monoclonal antibody #1 comprises the heavy chain variable region shown in SEQ ID NO: 44 and the light chain variable region shown in SEQ ID NO: 45; the monoclonal antibody #2 comprises the heavy chain variable region shown in SEQ ID NO: 44 and the light chain variable region shown in SEQ ID NO: 46; the monoclonal antibody #3 comprises the heavy chain variable region shown in SEQ ID NO: 44 and the light chain variable region shown in SEQ ID NO: 47; the monoclonal antibody #4 comprises the heavy chain variable region shown in SEQ ID NO: 44 and the light chain variable region shown in SEQ ID NO: 48; the monoclonal antibody #5 comprises the heavy chain variable region shown in SEQ ID NO: 49 and the light chain variable region shown in SEQ ID NO: 50; the monoclonal antibody #6 comprises the heavy chain variable region shown in SEQ ID NO: 51 and the light chain variable region shown in SEQ ID NO: 52; the monoclonal antibody #7 comprises the heavy chain variable region shown in SEQ ID NO: 53 and the light chain variable region shown in SEQ ID NO: 54; the monoclonal antibody #8 comprises the heavy chain variable region shown in SEQ ID NO: 55 and the light chain variable region shown in SEQ ID NO: 56; the monoclonal antibody #9 comprises the heavy chain variable region shown in SEQ ID NO: 57 and the light chain variable region shown in SEQ ID NO: 58; and the monoclonal antibody #10 comprises the heavy chain variable region shown in SEQ ID NO: 59 and the light chain variable region shown in SEQ ID NO: 60.

(2) Identification of Peptide in CAPRIN-1 to which Mouse Anti-Human CAPRIN-1 Antibody Reactive with Cancer Cell Surface Binds

The cancer cell surface-reactive mouse anti-human CAPRIN-1 monoclonal antibodies #1 to #10 obtained above were used to identify partial sequences in CAPRIN-1 recognized thereby.

First, DTT (Fluka) was added at a final concentration of 10 mM to 100 μL of a 1 μg/μL solution containing recombinant CAPRIN-1 dissolved in PBS, and reacted at 95° C. for 5 minutes to reduce disulfide bonds in the CAPRIN-1. Next, 20 mM (final concentration) iodoacetamide (Wako Pure Chemical Industries, Ltd.) was added thereto, followed by the alkylation reaction of thiol groups at 37° C. for 30 minutes under shading conditions. 50 μg each of the mouse anti-human CAPRIN-1 monoclonal antibodies #1 to #10 was added to 40 μg of the obtained reduced alkylated CAPRIN-1. The total amount of each mixture was adjusted to 1 mL with a 20 mM phosphate buffer solution (pH 7.0). The resulting mixture was reacted overnight at 4° C. while mixed by stirring.

Next, trypsin (Promega K.K.) was added at a final concentration of 0.2 μg to each reaction mixture and reacted at 37° C. for 1 hour, 2 hours, 4 hours, and 12 hours. Then, the reaction mixture was mixed with protein A-glass beads (GE Healthcare Bio-Sciences Ltd.) blocked with PBS containing 1% BSA (Sigma-Aldrich Corp.) and washed with PBS in advance, 1 mM calcium carbonate, and NP-40 buffer solution (20 mM phosphate buffer solution (pH 7.4), 5 mM EDTA, 150 mM NaCl, 1% NP-40) and reacted for 30 minutes.

Each reaction solution was washed with a 25 mM ammonium carbonate buffer solution (pH 8.0), followed by the elution of antigen-antibody complexes using 100 μL of 0.1% formic acid. The eluate was analyzed by LC-MS using Q-TOF Premier (Waters-MicroMass). This analysis followed the protocol attached to the instrument.

As a result, the polypeptide shown in SEQ ID NO: 61 was identified as a partial CAPRIN-1 sequence recognized by all of the mouse anti-human CAPRIN-1 monoclonal antibodies #1 to #10. In the polypeptide shown in SEQ ID NO: 61, the peptide shown in SEQ ID NO: 62 was further identified as a partial amino sequence recognized by the monoclonal antibodies #1 to #4, #5 to #7, and #9. The peptide shown in SEQ ID NO: 63 was further found to be recognized by the monoclonal antibody #10.

(3) Preparation of Chicken Anti-human CAPRIN-1 Monoclonal Antibody

300 μg of human CAPRIN-1 having the amino acid sequence shown in SEQ ID NO: 2 as prepared in Example 3 of WO2010/016526 was mixed with an equal amount of a complete Freund's adjuvant. This mixture was used as an antigen solution per chicken. The antigen solution was intraperitoneally administered to each 7-week-old chicken. Then, 7 boosters were performed every 4 weeks to complete immunization. Four days after the final shot, the spleen of each chicken was excised and ground between two sterilized glass slides. Procedures of washing with PBS(−) (Nissui Pharmaceutical Co., Ltd.) and removing the supernatant by centrifugation at 1500 rpm for 10 minutes were repeated three times to obtain spleen cells. The obtained spleen cells were mixed with light chain-deficient chicken myeloma cells established from chickens by transformation using avian reticuloendotheliosis virus, at a ratio of 5:1. 200 μL of an IMDM medium containing 10% FBS was heated to 37° C. and mixed with 800 μL of PEG1500 (Boehringer Ingelheim GmbH), and the PEG solution thus prepared was added to the cell mixture, which was then left standing for 5 minutes for cell fusion. After removal of the supernatant by centrifugation at 1700 rpm for 5 minutes, the cells were suspended in 300 mL of an IMDM medium containing 10% FBS supplemented with 2% equivalent of a HAT solution (Gibco) (HAT selective medium). This suspension was inoculated to thirty 96-well plates (Nunc) at 100 μL/well. The spleen cells and the chicken myeloma cells were fused by culture at 37° C. for 7 days under conditions of 5% CO₂ to obtain hybridomas.

The prepared hybridomas were screened with the binding affinity of antibodies produced by the hybridomas against CAPRIN-1 as an indicator. The 1 μg/mL CAPRIN-1 solution was added to a 96-well plate at 100 μL/well and left standing at 4° C. for 18 hours. Each well was washed three times with PBS-T. Then, a 0.5% bovine serum albumin (BSA) solution (Sigma-Aldrich Corp.) was added thereto at 400 μL/well and left standing at room temperature for 3 hours. The solution in each well was discarded, and each well was washed three times with 400 μL of PBS-T. Then, the culture supernatant of each hybridoma obtained above was added thereto at 100 μL/well and left standing at room temperature for 2 hours. Each well was washed three times with PBS-T. Then, HRP-labeled anti-chicken IgY antibodies (Sigma-Aldrich Corp.) diluted 5000-fold with PBS were added thereto at 100 μL/well and left standing at room temperature for 1 hour. Each well was washed three times with PBS-T. Then, a TMB substrate solution (Thermo Fisher Scientific Inc.) was added thereto at 100 μL/well and left standing for 15 to 30 minutes to cause color reaction. After the color development, the reaction was terminated by the addition of 1 N sulfuric acid at 100 μL/well. The absorbance was measured at 450 nm and 595 nm using an absorption spectrometer. As a result, several hybridomas producing antibodies having high absorbance were selected as candidate lines of the hybridoma of interest.

The selected hybridomas were added to a 96-well plate at a density of 0.5 cells/well and cultured in the plate. One week later, hybridomas forming single colonies in the wells were observed. The cells in these wells were further cultured, and the cloned hybridomas were screened with the binding affinity of antibodies produced by the hybridomas against CAPRIN-1 proteins as an indicator. As a result, a plurality of hybridoma lines producing monoclonal antibodies reactive with CAPRIN-1 proteins was obtained.

Next, these monoclonal antibodies were screened for antibodies reactive with the surface of breast cancer cells expressing CAPRIN-1. Specifically, 5×10⁵ cells of a human breast cancer cell line MDA-MB-231V were centrifuged in a 1.5-mL microcentrifuge tube. 100 μL of the culture supernatant of each hybridoma obtained above was added thereto and left standing for 1 hour on ice. After washing with PBS, FITC-labeled goat anti-chicken IgG (H+L) antibodies (SouthernBiotech) diluted 30-fold with PBS containing 0.1% FBS were added thereto and left standing for 1 hour on ice. After washing with PBS, the fluorescence intensity was measured using FACSCalibur (Becton, Dickinson and Company). On the other hand, the same operation as above was performed using a medium for hybridoma culture to prepare a control sample. As a result, 1 monoclonal antibody (chicken anti-human CAPRIN-1 monoclonal antibody #11) having stronger fluorescence intensity than that of the control, i.e., reactive with the surface of breast cancer cells expressing CAPRIN-1, was selected.

(4) Preparation of Mouse-Chicken Chimeric Recombinant Antibody

The gene amplification fragment of the heavy chain variable region (SEQ ID NO: 64) of the chicken anti-human CAPRIN-1 monoclonal antibody #11 obtained in the preceding paragraph (3) was treated at both ends with restriction enzymes, then purified, and inserted according to a routine method into a pcDNA4/myc-His (life Technologies, Inc.) vector already having gene inserts of a chicken antibody-derived leader sequence and a mouse IgG1 H chain constant region. Also, the gene amplification fragment of the light chain variable region (SEQ ID NO: 65) of the chicken anti-human CAPRIN-1 monoclonal antibody #11 was treated at both ends with restriction enzymes, then purified, and inserted according to a routine method into a pcDNA3.1/myc-His (life Technologies, Inc.) vector already having gene inserts of a chicken antibody-derived leader sequence and a mouse IgG1 L chain constant region.

Next, the recombinant vector having the gene insert of the heavy chain variable region of the chicken anti-human CAPRIN-1 monoclonal antibody #11 and the recombinant vector having the gene insert of the light chain variable region of the chicken anti-human CAPRIN-1 monoclonal antibody #11 were introduced into CHO-K1 cells (obtained from Riken Cell Bank). Specifically, 2×10⁵ CHO-K1 cells were cultured in 1 mL of a Ham's F12 medium (life Technologies, Inc.) containing of 10% FBS per well of a 12-well culture plate, and washed with PBS(−). Then, a fresh Ham's F12 medium containing 1 mL of 10% FBS per well was added thereto. 250 ng each of the vectors dissolved in 30 μL of OptiMEM (life Technologies, Inc.) was mixed with 30 μL of Polyfect transfection reagent (Qiagen N.V.), and this mixture was added to each well. The CHO-K1 cells cotransfected with the recombinant vectors were cultured in a Ham's F12 medium containing 10% FBS supplemented with 200 μg/mL Zeocin (life Technologies, Inc.) and 200 μg/mL Geneticin (Roche Diagnostics K.K.) and then inoculated to a 96-well plate at a density of 0.5 cells/well to prepare a cell line stably producing a mouse-chicken chimeric anti-human CAPRIN-1 monoclonal antibody #12 having the variable regions of the chicken monoclonal antibody #11 and the constant regions of mouse IgG1. The prepared cell line was cultured for 5 days in a 150-cm² flask at a density of 5×10⁵ cells/mL using 30 mL of a serum-free OptiCHO medium (life Technologies, Inc.) to obtain a culture supernatant containing #12.

(5) Identification of CAPRIN-1 Epitope Recognized by Mouse-chicken Chimeric Anti-Human CAPRIN-1 Monoclonal Antibody #12

The cancer cell surface-reactive mouse-chicken chimeric anti-human CAPRIN-1 monoclonal antibody #12 obtained in the paragraph (4) was used to identify a CAPRIN-1 epitope region recognized thereby. 100 μg of recombinant CAPRIN-1 proteins was dissolved in a protein inhibitor-free dissolving buffer and reacted with the monoclonal antibody #12. To this solution, a digestive enzyme trypsin or chymotrypsin was added, followed by digestion reaction at a proper temperature. After the reaction, a protein G Sepharose carrier was added thereto, then reacted, and precipitated by centrifugation operation. After removal of the supernatant, the carrier was washed with a dissolving buffer and PBS and dissolved in 0.1% formic acid, and the supernatant was recovered. The recovered supernatant sample was applied to a reverse-phase column (HLB Extraction Cartridge (Waters-OASIS)) to obtain an antibody-free sample solution. The obtained sample was subjected to reverse-phase liquid chromatography (Chromatography Nanosytem (KYA Technologies Corp.)) to recover a solution containing only peptides. The solution was introduced to a tandem-type mass spectrometer Quadrupole-TOF Mass Spectrometer (Waters-MicroMass) and analyzed by MS/MS to detect the peptides contained in the sample. As a result, a peptide consisting of the amino acid sequence shown in SEQ ID NO: 66 was identified as a partial CAPRIN-1 sequence recognized by the mouse-chicken chimeric anti-human CAPRIN-1 monoclonal antibody #12. Also, this peptide refers to a partial CAPRIN-1 sequence recognized by the chicken anti-human CAPRIN-1 monoclonal antibody #11 constituting the variable regions of the antibody #12.

(6) Preparation of Human-chicken Chimeric Anti-human CAPRIN-1 Antibody

The gene amplification fragment of the heavy chain variable region (SEQ ID NO: 64) of the chicken anti-human CAPRIN-1 monoclonal antibody #11 obtained in the preceding paragraph (3) was treated at both ends with restriction enzymes, then purified, and inserted according to a routine method into a pcDNA4/myc-His (life Technologies, Inc.) vector already having gene inserts of a chicken antibody-derived leader sequence comprising SEQ ID NO: 67 and a human IgG1 H chain constant region comprising SEQ ID NO: 68. Also, the gene amplification fragment of the light chain variable region (SEQ ID NO: 65) of the chicken anti-human CAPRIN-1 monoclonal antibody #11 was treated at both ends with restriction enzymes, then purified, and inserted according to a routine method into a pcDNA3.1/myc-His (life Technologies, Inc.) vector already having gene inserts of a chicken antibody-derived leader sequence comprising SEQ ID NO: 68 and a human IgG1 L chain constant region comprising SEQ ID NO: 69.

Next, the recombinant vector having the gene insert of the heavy chain variable region of the antibody #11 above and the recombinant vector having the gene insert of the light chain variable region of the antibody #11 above were introduced into CHO-K1 cells (obtained from Riken Cell Bank). Specifically, 2×10⁵ CHO-K1 cells were cultured in 1 mL of a Ham's F12 medium (life Technologies, Inc.) containing 10% FBS per well of a 12-well culture plate, and washed with PBS(−). Then, a fresh Ham's F12 medium containing 1 mL of 10% FBS per well was added thereto. 250 ng each of the vectors dissolved in 30 μL of OptiMEM (life Technologies, Inc.) was mixed with 30 μL of Polyfect transfection reagent (Qiagen N.V.), and this mixture was added to each well. The CHO-K1 cells cotransfected with the recombinant vectors were cultured in a Ham's F12 medium containing 10% FBS supplemented with 200 μg/mL Zeocin (life Technologies, Inc.) and 200 μg/mL Geneticin (Roche Diagnostics K.K.) and then inoculated to a 96-well plate at a density of 0.5 cells/well to prepare a cell line stably producing a human-chicken chimeric anti-human CAPRIN-1 antibody #13 having the variable regions of the chicken anti-human CAPRIN-1 monoclonal antibody #11 and the constant regions of human IgG1. The prepared cell line was cultured for 5 days in a 150-cm² flask at a density of 5×10⁵ cells/mL using 30 mL of a serum-free OptiCHO medium (life Technologies, Inc.) to obtain a culture supernatant containing the antibody #13 above.

(7) Preparation of Mouse Anti-human CAPRIN-1 Monoclonal Antibody #14

In the same way as in the paragraph (1), a fusion protein of the amino acid sequence shown in SEQ ID NO: 63 identified in the paragraph (2) and a carrier protein KLH (keyhole limpet hemocyanin) was mixed as an immunogen with an equal amount of an adjuvant TiterMax Gold® (CytRx Corp.), and this mixture was subcutaneously administered at a dose of 20 μg/shot to each mouse at 7-day intervals. After administration with four shots in total, spleen cells were obtained from the mouse 3 days after the final immunization and fused with mouse myeloma cells in the same way as in the paragraph (1) to prepare hybridomas. Then, antibodies were screened using, as an indicator, the reactivity of each antibody contained in the culture supernatants of the prepared hybridomas with a 1 μg/mL solution of CAPRIN-1 prepared in Example 3 of WO2010/016526 or a fusion protein of the amino acid sequence shown in SEQ ID NO: 63 used as an immunogen and a carrier protein KLH. The 1 μg/mL CAPRIN-1 solution prepared in Example 3 of WO2010/016526 and the fusion protein (30 μg/mL) of the amino acid sequence shown in SEQ ID NO: 63 and a carrier protein BSA were separately added at 100 μL/well to 96-well plates and left standing at 4° C. for 18 hours. Each well was washed with PBS-T. Then, a Block Ace (DS Pharma Biomedical Co., Ltd.) solution was added thereto at 400 μL/well and left standing at room temperature for 3 hours. The solution in each well was removed, and each well was washed with PBS-T. Then, the culture supernatant of each hybridoma obtained above was added thereto at 100 μL/well and left standing at room temperature for 2 hours. Each well was washed with PBS-T. Then, HRP-labeled anti-mouse IgG (H+L) antibodies (life Technologies, Inc.) diluted 5000-fold with PBS were added thereto at 100 μL/well and left standing at room temperature for 1 hour. Each well was washed with PBS-T. Then, a TMB substrate solution (Thermo Fisher Scientific Inc.) was added thereto at 100 μL/well and left standing for 5 to 30 minutes to cause color reaction. After the color development, the reaction was terminated by the addition of 1 N sulfuric acid at 100 μL/well. The absorbance was measured at 450 nm and 595 nm using an absorption spectrometer. As a result, hybridomas producing antibodies having high absorbance were selected.

The selected hybridomas were added to a 96-well plate at a density of 0.3 cells/well and cultured in the plate. One week later, hybridomas forming single colonies in the wells were observed. The cells in these wells were further cultured, and the cloned hybridomas were screened in the same way as above with the binding affinity of antibodies produced by the hybridomas against the amino acid sequence shown in SEQ ID NO: 63 as a partial CAPRIN-1 sequence as an indicator to obtain hybridomas producing antibodies against the amino acid of SEQ ID NO: 63.

Monoclonal antibodies produced by the obtained hybridomas were screened for antibodies reactive with the surface of breast cancer cells expressing CAPRIN-1. Specifically, 10⁶ cells of a human breast cancer cell line MDA-MB-231V were centrifuged in a 1.5-mL microcentrifuge tube. 100 μL of the culture supernatant of each hybridoma obtained above was added thereto and left standing for 1 hour on ice. After washing with PBS, FITC-labeled goat anti-mouse IgG antibodies (Life Technologies, Inc.) diluted 500-fold with PBS containing 0.1% FBS were added thereto and left standing for 1 hour on ice. After washing with PBS, the fluorescence intensity was measured using FACSCalibur (Becton, Dickinson and Company). On the other hand, the same operation as above was performed using instead of the antibodies a sample composed of the serum of each untreated 6-week-old Balb/c mouse diluted 500-fold with a medium for hybridoma culture and a negative control sample composed of cells reacted only with secondary antibodies. As a result, a mouse anti-human CAPRIN-1 monoclonal antibody #14 having stronger fluorescence intensity than that of the negative control, i.e., reactive with the surface of breast cancer cells, was obtained. The antibody #14 consists of the heavy chain variable region shown in SEQ ID NO: 70 and the light chain variable region shown in SEQ ID NO: 71.

The obtained mouse anti-human CAPRIN-1 monoclonal antibody #14 was examined for its specific reaction with the amino acid sequence shown in SEQ ID NO: 63 as a partial CAPRIN-1 sequence used as an immunogen. A 30 μg/mL solution consisting of the amino acid sequence shown in SEQ ID NO: 63 prepared with a 0.1 M aqueous sodium carbonate solution and a similar 30 μg/mL consisting of a partial CAPRIN-1 sequence free from the amino acid sequence shown in SEQ ID NO: 63 were separately added to 96-well plates Immobilizer Amino for ELISA (Thermo Fisher Scientific Inc./Nunc) at 100 μg/mL and reacted all night and all day at 4° C. to bind the peptides to the wells. A 0.1 M aqueous sodium carbonate solution containing 10 mM ethanolamine was added to each peptide-bound well and left standing at room temperature for 1 hour. The solution in each well was removed, and each well was then washed with PBS-T. Then, a Block Ace solution was added thereto at 400 μL/well and left standing at room temperature for 3 hours. The solution in each well was removed, and each well was washed with PBS-T. Then, the culture supernatant containing the mouse monoclonal antibody #14 was added thereto at 50 μL/well and reacted at room temperature for 1 hour. Then, each well was washed with PBS-T, and HRP-labeled anti-mouse IgG (H+L) antibodies (life Technologies, Inc.) diluted 5000-fold with a Block Ace solution were added thereto at 50 μL/well and left standing at room temperature for 1 hour. Each well was fully washed with PBS-T. Then, a TMB substrate solution (Thermo Fisher Scientific Inc.) was added thereto at 100 μL/well and left standing for 5 to 30 minutes to cause color reaction. After the color development, the reaction was terminated by the addition of 1 N sulfuric acid at 100 μL/well. The absorbance was measured at 450 nm and 595 nm using an absorption spectrometer. As a result, the mouse monoclonal antibody #14 did not react with the partial CAPRIN-1 sequence free from the amino acid sequence shown in SEQ ID NO: 63, but specifically reacted only with the amino acid sequence shown in SEQ ID NO: 63. Thus, the polypeptide shown in SEQ ID NO: 63 was confirmed to contain an epitope region recognized by the anti CAPRIN-1 antibody #14.

Example 3 Selection of Optimum Antibody for CAPRIN-1 Detection

(1) Selection of Antibody Using Human Breast Cancer Tissue

31 breast cancer tissue samples of paraffin-embedded human breast cancer tissue arrays (Medical & Biological Laboratories Co., Ltd.) were used in immunohistochemical staining. Each human breast cancer tissue array was treated at 60° C. for 3 hours and then placed in a staining bottle filled with said xylene, and procedures of replacing xylene with a fresh one every 5 minutes were performed three times. Subsequently, the same operation as in xylene was performed using ethanol and PBS-T. The human breast cancer tissue array was placed in a staining bottle filled with a 10 mM citrate buffer solution (pH 6.0) containing 0.05% Tween 20, treated at 125° C. for 5 minutes, and then left standing at room temperature for 40 minutes or longer. Excess water around sections was wiped off with Kimwipe. The section on each glass slide was encircled with a Dako pen (Dako, an Agilent Technologies Company), and an appropriate amount of Peroxidase Block (Dako, an Agilent Technologies Company) was added dropwise thereto. The glass slide was left standing at room temperature for 5 minutes and then placed in a staining bottle filled with PBS-T, and procedures of replacing PBS-T with a fresh one every 5 minutes were performed three times. A PBS-T solution containing 10% FBS was applied thereto as a blocking solution, and the glass slide was left standing at room temperature for 1 hour in a moist chamber. Next, 10 μg/mL of the mouse anti-human CAPRIN-1 monoclonal antibody #8 or #14 prepared in Example 2 in a PBS-T solution containing 5% FBS was applied thereto. The glass slide was left standing overnight at 4° C. in a moist chamber. After washing with PBS-T for 10 minutes three times, an appropriate amount of Peroxidase Labelled Polymer Conjugated (Dako, an Agilent Technologies Company) was added dropwise thereto, and the glass slide was left standing at room temperature for 30 minutes in a moist chamber. After washing with PBS-T for 10 minutes three times, a DAB staining solution (Dako, an Agilent Technologies Company) was applied thereto, and the glass slide was left standing at room temperature for approximately 10 minutes. Then, the staining solution was discarded, and the glass slide was washed with PBS-T for 10 minutes three times. After rinsing with distilled water, the glass slide was placed in 70%, 80%, 90%, 95%, and 100% ethanol solutions in this order for 1 minute per solution, and finally left standing overnight in xylene. The glass slide was taken out and the section was embedded in Glycergel Mounting Medium (Dako, an Agilent Technologies Company), followed by observation. The expression level of CAPRIN-1 in the tissues was evaluated according to the criteria given below. A slide that exhibited positive results was selected, and its CAPRIN-1 stain image was observed. First, the CAPRIN-1 stain image of cancer cells in the tissues, the intensity of positive staining, and the ratio of positive cells were observed by use of a ×4 objective lens of a light microscope. Next, the objective lens was changed to a ×10 or ×20 lens, and examination was made on whether the positive results were localized to the cell membrane or the cytoplasm. The detection results were evaluated by these methods and classified into scores 0 to 3. The details of the scores are as follows:

Score 0 (without CAPRIN-1 overexpression): Positive staining of the cell membrane is not observed or is observed in less than 10% of the cancer cells.

Score 1 (without CAPRIN-1 overexpression): Faint, almost unperceivable staining of the cell membrane is observed in 10% or more of the cancer cells, and these cancer cells are partially stained only at their cell membranes.

Score 2 (with CAPRIN-1 overexpression): Weak to moderate complete positive staining of the cell membrane is observed in 10% or more of the cancer cells, or strong complete positive staining of the cell membrane is observed in 10% or more and 30% or less of the cancer cells.

Score 3 (with CAPRIN-1 overexpression): Strong complete positive staining of the cell membrane is observed in 30% or more of the cancer cells.

A tissue is determined as CAPRIN-1-positive cancer tissue, when its assay results are given score 2 and 3.

As a result, the expression of CAPRIN-1 in the breast cancer tissues was successfully observed using both of the antibodies. The results of immunohistochemical staining using the antibody #8 exhibited score 2 for 14 samples and score 3 for 1 sample, and the number of CAPRIN-1-positive samples was 15 samples. By contrast, the result of immunohistochemical staining using the antibody #14 exhibited score 2 for 12 samples and score 3 for 8 samples, and the number of CAPRIN-1-positive samples was 20 samples. Thus, the more highly sensitive antibody #14 was selected for the detection of CAPRIN-1 using human cancer tissues.

(2) Detection of CAPRIN-1 on Various Human Normal Tissues by Immunohistochemical Staining Method Using Antibody #14

Human normal tissue array (US Biomax, Inc.) (including brain, thyroid gland, lung, spleen, kidney, esophagus, stomach, large bowel, pancreas, muscle, skin, salivary gland, ovary, uterus, mammary gland, placenta, bone marrow, testis, and prostate tissues) was used in immunohistochemical staining. Excess water around a section was wiped off with Kimwipe. The section on the glass slide was encircled with a Dako pen (Dako, an Agilent Technologies Company), and an appropriate amount of Peroxidase Block (Dako, an Agilent Technologies Company) was added dropwise thereto. The glass slide was left standing at room temperature for 5 minutes and then placed in a staining bottle filled with PBS-T, and procedures of replacing PBS-T with a fresh one every 5 minutes were performed three times. A PBS-T solution containing 10% FBS was applied thereto as a blocking solution, and the glass slide was left standing at room temperature for 1 hour in a moist chamber. Next, 10 μg/mL of the mouse anti-human CAPRIN-1 monoclonal antibody #14 prepared in Example 2 in a PBS-T solution containing 5% FBS, and this solution was applied thereto. The glass slide was left standing overnight at 4° C. in a moist chamber. After washing with PBS-T for 10 minutes three times, an appropriate amount of Peroxidase Labelled Polymer Conjugated (Dako, an Agilent Technologies Company) was added dropwise thereto, and the glass slide was left standing at room temperature for 30 minutes in a moist chamber. After washing with PBS-T for 10 minutes three times, a DAB staining solution (Dako, an Agilent Technologies Company) was applied thereto, and the glass slide was left standing at room temperature for approximately 10 minutes. Then, the staining solution was discarded, and the glass slide was washed with PBS-T for 10 minutes three times. After rinsing with distilled water, the glass slide was placed in 70%, 80%, 90%, 95%, and 100% ethanol solutions in this order for 1 minute per solution, and finally left standing overnight in xylene. The glass slide was taken out and enclosed in Glycergel Mounting Medium (Dako, an Agilent Technologies Company), followed by observation.

The expression level of CAPRIN-1 in the tissues was evaluated according to the criteria given below. A slide that exhibited positive results was selected, and its CAPRIN-1 stain image was confirmed. First, the CAPRIN-1 stain image of cancer cells in the tissues, the intensity of positive staining, and the ratio of positive cells were observed by use of a ×4 objective lens of a light microscope. Next, the objective lens was changed to a ×10 or ×20 lens, and examination was made on whether the positive results were derived from the cell membrane or localized to the cytoplasm. The detection results were evaluated by these methods and classified into scores 0 to 3. The details of the scores are as follows:

Score 0 (without CAPRIN-1 overexpression): Positive staining of the cell membrane is not observed or is observed in less than 10% of the cancer cells.

Score 1 (without CAPRIN-1 overexpression): Faint, almost unperceivable staining of the cell membrane is observed in 10% or more of the cancer cells, and these cancer cells are partially stained only at their cell membranes.

Score 2 (with CAPRIN-1 overexpression): Weak to moderate complete positive staining of the cell membrane is observed in 10% or more of the cancer cells, or strong complete positive staining of the cell membrane is observed in 10% or more and 30% or less of the cancer cells.

Score 3 (with CAPRIN-1 overexpression): Strong complete positive staining of the cell membrane is observed in 30% or more of the cancer cells.

A tissue was determined as CAPRIN-1-positive cancer tissue, when its detection results were given score 2 or 3.

The uterus and prostate tissues were given score 1, whereas the other tissues were all given score 0. Thus, the expression of CAPRIN-1 was not observed in the human normal tissues.

(3) Detection of CAPRIN-1 on Various Human Cancer Tissues by Immunohistochemical Staining Method Using Mouse Anti-human CAPRIN-1 Antibody #14

Various cancer tissues of paraffin-embedded human cancer tissue arrays (US Biomax, Inc.) were used in immunohistochemical staining. Each human cancer tissue array was treated at 60° C. for 3 hours and then placed in a staining bottle filled with xylene, and procedures of replacing said xylene with a fresh one every 5 minutes were performed three times. Subsequently, the same operation as in xylene was performed using ethanol and PBS-T. The human cancer tissue array was placed in a staining bottle filled with a 10 mM citrate buffer solution (pH 6.0) containing 0.05% Tween 20, treated at 125° C. for 5 minutes, and then left standing at room temperature for 40 minutes or longer. Excess water around sections was wiped off with Kimwipe. The section on each glass slide was encircled with a Dako pen (Dako, an Agilent Technologies Company), and an appropriate amount of Peroxidase Block (Dako, an Agilent Technologies Company) was added dropwise thereto. The glass slide was left standing at room temperature for 5 minutes and then placed in a staining bottle filled with PBS-T, and procedures of replacing PBS-T with a fresh one every 5 minutes were performed three times. A PBS-T solution containing 10% FBS was applied thereto as a blocking solution, and the glass slide was left standing at room temperature for 1 hour in a moist chamber. Next, 10 μg/mL of the monoclonal antibody #14 prepared in Example 2 in a PBS-T solution containing 5% FBS, and this solution was applied thereto. The glass slide was left standing overnight at 4° C. in a moist chamber. After washing with PBS-T for 10 minutes three times, an appropriate amount of Peroxidase Labelled Polymer Conjugated (Dako, an Agilent Technologies Company) was added dropwise thereto, and the glass slide was left standing at room temperature for 30 minutes in a moist chamber. After washing with PBS-T for 10 minutes three times, a DAB staining solution (Dako, an Agilent Technologies Company) was applied thereto, and the glass slide was left standing at room temperature for approximately 10 minutes. Then, the staining solution was discarded, and the glass slide was washed with PBS-T for 10 minutes three times. The glass slide was rinsed with distilled water and placed in 70%, 80%, 90%, 95%, and 100% ethanol solutions in this order for 1 minute per solution, and finally left standing overnight in xylene. The glass slide was taken out and enclosed in Glycergel Mounting Medium (Dako, an Agilent Technologies Company), followed by observation.

The expression level of CAPRIN-1 in the tissues was evaluated according to the criteria given below. A slide that exhibited positive results was selected, and its CAPRIN-1 stain image was confirmed. First, the CAPRIN-1 stain image of cancer cells in the tissues, the intensity of positive staining, and the ratio of positive cells were observed by use of a ×4 objective lens of a light microscope. Next, the objective lens was changed to a ×10 or ×20 lens, and examination was made on whether the positive results were derived from the cell membrane or localized to the cytoplasm. The detection results were evaluated by these methods and classified into scores 0 to 3. The details of the scores are as follows:

Score 0 (without CAPRIN-1 overexpression): Positive staining of the cell membrane is not observed or is observed in less than 10% of the cancer cells.

Score 1 (without CAPRIN-1 overexpression): Faint, almost unperceivable staining of the cell membrane is observed in 10% or more of the cancer cells, and these cancer cells are partially stained only at their cell membranes.

Score 2 (with CAPRIN-1 overexpression): Weak to moderate complete positive staining of the cell membrane is observed in 10% or more of the cancer cells, or strong complete positive staining of the cell membrane is observed in 10% or more and 30% or less of the cancer cells.

Score 3 (with CAPRIN-1 overexpression): Strong complete positive staining of the cell membrane is observed in 30% or more of the cancer cells.

A tissue is determined as CAPRIN-1-positive cancer tissue, when its assay results are given score 2 or 3.

As a result, CAPRIN-1 was confirmed to be positive in each of 16 out of 22 brain tumor tissue samples (64%), 19 out of 32 lung cancer tissue samples (59%), 18 out of 21 uterus cancer tissue samples (86%), 10 out of 16 esophagus cancer tissue samples (63%), 27 out of 30 kidney cancer tissue samples (90%), 14 out of 17 liver cancer tissue samples (82%), 11 out of 15 thyroid gland cancer tissue samples (73%), 10 out of 14 stomach cancer tissue samples (71%), 17 out of 19 pancreas cancer tissue samples (89%), 13 out of 13 prostate cancer tissue samples (100%), 12 out of 14 bladder cancer tissue samples (86%), 11 out of 14 large bowel cancer tissue samples (79%), 24 out of 30 skin cancer tissue samples (80%), and 16 out of 21 breast cancer tissue samples (76%).

(4) Detection of CAPRIN-1 Protein on Dog Breast Cancer Tissue by Immunohistochemical Staining Method Using Mouse Anti-human CAPRIN-1 Antibody #14

100 frozen breast cancer tissue samples of dogs pathologically diagnosed as malignant breast cancer were used in immunohistochemical staining. Each frozen dog breast cancer tissue was sliced into 10 to 20 μm using Cryostat (Leica Biosystems), placed on a glass slide, and dried in air, together with the glass slide, for 30 minutes using a hair dryer to prepare a glass slide with a tissue slice placed thereon. Next, the glass slide was placed in a staining bottle filled with PBS-T (saline containing 0.05% Tween 20), and procedures of replacing PBS-T with a fresh one every 5 minutes were performed three times. Excess water around sections was wiped off with Kimwipe. The section on the glass slide was encircled with a Dako pen (Dako, an Agilent Technologies Company). Then, a PBS-T solution containing 10% fetal bovine serum was applied thereto as a blocking solution, and the glass slide was left standing at room temperature for 1 hour in a moist chamber. Next, 10 μg/mL of the mouse anti-human CAPRIN-1 monoclonal antibody #8 or #14 prepared in Example 2 in a blocking solution, and this solution was applied thereto. The glass slide was left standing overnight at 4° C. in a moist chamber. After washing with PBS-T for 10 minutes three times, MOM biotin-labeled anti-IgG antibodies (Vectastain) diluted 250-fold with a blocking solution were applied thereto, and the glass slide was left standing at room temperature for 1 hour in a moist chamber. After washing with PBS-T for 10 minutes three times, avidin-biotin ABC reagent (Vectastain) was applied thereto, and the glass slide was left standing at room temperature for 5 minutes in a moist chamber. After washing with PBS-T for 10 minutes three times, a DAB staining solution (10 mg of DAB+10 μL of 30% H₂O₂/50 mL of 0.05 M Tris-HCl (pH 7.6)) was applied thereto, and the glass slide was left standing at room temperature for 30 minutes in a moist chamber. The glass slide was rinsed with distilled water. A hematoxylin reagent (Dako, an Agilent Technologies Company) was applied thereto, and the glass slide was left standing at room temperature for 1 minute and then rinsed with distilled water. The glass slide was placed in 70%, 80%, 90%, 95%, and 100% ethanol solutions in this order for 1 minute per solution, and finally left standing overnight in xylene. The glass slide was taken out and enclosed in Glycergel Mounting Medium (Dako, an Agilent Technologies Company), followed by observation. The expression level of CAPRIN-1 in the tissues was evaluated according to the criteria given below. A slide that exhibited positive results was selected, and its CAPRIN-1 stain image was confirmed. First, the CAPRIN-1 stain image of cancer cells in the tissues, the intensity of positive staining, and the ratio of positive cells were observed by use of a ×4 objective lens of a light microscope. Next, the objective lens was changed to a ×10 or ×20 lens, and examination was made on whether the positive results were derived from the cell membrane or localized to the cytoplasm. The detection results were evaluated by these methods and classified into scores 0 to 3. The details of the scores are as follows:

Score 0 (without CAPRIN-1 overexpression): Positive staining of the cell membrane is not observed or is observed in less than 10% of the cancer cells.

Score 1 (without CAPRIN-1 overexpression): Faint, almost unperceivable staining of the cell membrane is observed in 10% or more of the cancer cells, and these cancer cells are partially stained only at their cell membranes.

Score 2 (with CAPRIN-1 overexpression): Weak to moderate complete positive staining of the cell membrane is observed in 10% or more of the cancer cells, or strong complete positive staining of the cell membrane is observed in 10% or more and 30% or less of the cancer cells.

Score 3 (with CAPRIN-1 overexpression): Strong complete positive staining of the cell membrane is observed in 30% or more of the cancer cells.

A cancer-bearing dog tissue was confirmed to be CAPRIN-1-positive and to get effective therapeutic effects by the administration of a therapeutic drug targeting CAPRIN-1, when its assay results were given score 2 or 3.

As a result, the expression of CAPRIN-1 in the dog breast cancer tissues was successfully observed using both of the antibodies. Specifically, the results of immunohistochemical staining using the antibody #8 exhibited score 2 for 69 samples and score 3 for 11 samples, and the number of CAPRIN-1-positive samples was 80 samples (80%). By contrast, the result of immunohistochemical staining using the antibody #14 exhibited score 2 for 50 samples and score 3 for 32 samples, and the number of CAPRIN-1-positive samples was 82 samples (82%).

(5) Detection of CAPRIN-1 on Cat Breast Cancer Tissue by Immunohistochemical Staining Method Using Mouse Anti-human CAPRIN-1 Monoclonal Antibody #14

30 frozen breast cancer tissue samples of cats pathologically diagnosed as malignant breast cancer were used in immunohistochemical staining. Each frozen cat cancer tissue was sliced into 10 to 20 μm using Cryostat (Leica Biosystems), placed on a glass slide, and dried in air, together with the glass slide, for 30 minutes using a hair dryer to prepare a glass slide with a tissue slice placed thereon. Next, the glass slide was placed in a staining bottle filled with PBS-T (saline containing 0.05% Tween 20), and procedures of replacing PBS-T with a fresh one every 5 minutes were performed three times. Excess water around sections was wiped off with Kimwipe. The section on the glass slide was encircled with a Dako pen (Dako, an Agilent Technologies Company). Then, a PBS-T solution containing 10% fetal bovine serum was applied thereto as a blocking solution, and the glass slide was left standing at room temperature for 1 hour in a moist chamber. Next, 10 μg/mL of the mouse anti-human CAPRIN-1 monoclonal antibody #8 or #14 prepared in Example 2 in a blocking solution, and this solution was applied thereto. The glass slide was left standing overnight at 4° C. in a moist chamber. After washing with PBS-T for 10 minutes three times, MOM biotin-labeled anti-IgG antibodies (Vectastain) diluted 250-fold with a blocking solution were applied thereto, and the glass slide was left standing at room temperature for 1 hour in a moist chamber. After washing with PBS-T for 10 minutes three times, avidin-biotin ABC reagent (Vectastain) was applied thereto, and the glass slide was left standing at room temperature for 5 minutes in a moist chamber. After washing with PBS-T for 10 minutes three times, a DAB staining solution (10 mg of DAB+10 μL of 30% H₂O₂/50 ml of 0.05 M Tris-HCl (pH 7.6)) was applied thereto, and the glass slide was left standing at room temperature for 30 minutes in a moist chamber. The glass slide was rinsed with distilled water. A hematoxylin reagent (Dako, an Agilent Technologies Company) was applied thereto, and the glass slide was left standing at room temperature for 1 minute and then rinsed with distilled water. The glass slide was placed in 70%, 80%, 90%, 95%, and 100% ethanol solutions in this order for 1 minute per solution, and finally left standing overnight in xylene. The glass slide was taken out and enclosed in Glycergel Mounting Medium (Dako, an Agilent Technologies Company), followed by observation. The expression level of CAPRIN-1 in the tissues was evaluated according to the criteria given below. A slide that exhibited positive results was selected, and its CAPRIN-1 stain image was confirmed. First, the CAPRIN-1 stain image of cancer cells in the tissues, the intensity of positive staining, and the ratio of positive cells were observed by use of a ×4 objective lens of a light microscope. Next, the objective lens was changed to a ×10 or ×20 lens, and examination was made on whether the positive results were derived from the cell membrane or localized to the cytoplasm. The detection results were evaluated by these methods and classified into scores 0 to 3. The details of the scores are as follows:

Score 0 (without CAPRIN-1 overexpression): Positive staining of the cell membrane is not observed or is observed in less than 10% of the cancer cells.

Score 1 (without CAPRIN-1 overexpression): Faint, almost unperceivable staining of the cell membrane is observed in 10% or more of the cancer cells, and these cancer cells are partially stained only at their cell membranes.

Score 2 (with CAPRIN-1 overexpression): Weak to moderate complete positive staining of the cell membrane is observed in 10% or more of the cancer cells, or strong complete positive staining of the cell membrane is observed in 10% or more and 30% or less of the cancer cells.

Score 3 (with CAPRIN-1 overexpression): Strong complete positive staining of the cell membrane is observed in 30% or more of the cancer cells.

A cancer-bearing cat tissue was confirmed to be CAPRIN-1-positive and to get effective therapeutic effects by the administration of a therapeutic drug targeting CAPRIN-1, when its assay results were given score 2 or 3.

As a result, the expression of CAPRIN-1 in the cat breast cancer tissues was successfully observed using both of the antibodies. Specifically, the results of immunohistochemical staining using the antibody #8 exhibited score 2 for 20 samples and score 3 for 4 samples, and the number of CAPRIN-1-positive samples was 24 samples (80%). By contrast, the result of immunohistochemical staining using the antibody #14 exhibited score 2 for 18 samples and score 3 for 6 samples, and the number of CAPRIN-1-positive samples was 27 samples (90%).

Example 4 Correlation of CAPRIN-1 Expression Evaluated Using Cancer Sample with Antitumor Effect of Anti-CAPRIN-1 Antibody

(1) Detection of CAPRIN-1 by Immunohistochemical Staining Method Using Cancer Tissue Derived from Cancer-bearing Mouse in which Mouse Cancer Cell was Transplanted

Two mouse-derived cancer cell lines (B16F10 and EMT-6) were subcutaneously transplanted (each for 5 mice) into the dorsal regions of 26 Balb/c mice (Japan SLC, Inc.) and grown until the size of tumor became approximately 7 mm in diameter. Three subjects were selected from each of these two mouse groups respectively having the 2 types of cancer cell transplants. A tumor mass was excised from each mouse, cut open in PBS, and perfusion-fixed overnight in a 0.1 M phosphate buffer solution (pH 7.4) containing 4% paraformaldehyde (PFA). The perfusate was discarded, and the tissue surface of each organ was rinsed with PBS. A PBS solution containing 10% sucrose was added to a 50-mL centrifuge tube, in which each cancer tissue was then placed and shaken at 4° C. for 2 hours using a rotor. The solution was replaced with a PBS solution containing 20% sucrose, and again, the resulting solution was left standing at 4° C. until the cancer tissue was precipitated. Then, the solution was replaced with a PBS solution containing 30% sucrose, and the resulting solution was left standing at 4° C. until the cancer tissue was precipitated. The cancer tissue was taken out, and necessary portions were cut off with a surgical knife. Next, OCT compound (Tissue Tek) was poured onto the tissue surface and spread over the surface. Then, the tissue was disposed on Cryomold. The Cryomold was placed on dry ice, and the tissue was quickly frozen, then sliced into 10 to 20 μm using Cryostat (Leica Biosystems), placed on a glass slide, and dried in air, together with the glass slide, for 30 minutes using a hair dryer to prepare a glass slide with a tissue slice placed thereon. On the next day, the glass slide was washed with PBS(−) three times. PBS(−) containing 5% goat serum was applied thereto as a blocking solution, and the glass slide was left standing at room temperature for 1 hour in a moist chamber. Next, 10 μg/mL of the mouse anti-human CAPRIN-1 monoclonal antibody #8 or #14 prepared in Example 2 in a PBS(−) solution, and this solution was applied thereto. The glass slide was left standing overnight at 4° C. in a moist chamber. After washing with PBS(−) for 5 minutes five times, an appropriate amount of Peroxidase Labelled Polymer Conjugated (Dako, an Agilent Technologies Company) was added dropwise thereto, and the glass slide was left standing at room temperature for 30 minutes in a moist chamber. After washing with PBS-T for 5 minutes six times, a DAB staining solution (Dako, an Agilent Technologies Company) was applied thereto, and the glass slide was left standing at room temperature for approximately 10 minutes. Then, the staining solution was discarded, and the glass slide was washed with PBS(−) for 5 minutes three times. Then, the glass slide was enclosed in Glycergel Mounting Medium (Dako, an Agilent Technologies Company), followed by observation. As a result of scoring as described in Example 3, the results of immunohistochemical staining using the antibody #8 exhibited score 1 both for the melanoma-derived cancer cells B16F10 and for the breast cancer-derived cells EMT-6. Thus, CAPRIN-1 expression was not detected. On the other hand, the results of immunohistochemical staining using the antibody #14 exhibited score 1 for the cancer cells B16F10, as with the antibody #8, but exhibited score 3 for the cancer cells EMT-6.

(2) Antitumor Effect of Anti-CAPRIN-1 Antibody

The human-chicken chimeric anti-human CAPRIN-1 antibody #13 was studied for its antitumor effect using the cancer-bearing mice prepared in the preceding paragraph (1). Of 10 cancer-bearing mice in which each cancer cell line (B16F10 and EMT-6) was transplanted, 5 cancer-bearing mice in each group underwent the intraperitoneal administration of the antibody #13 at a dose of 200 μg (200 μL) per mouse. Then, the antibody was intraperitoneally administered at the same dose as above to each cancer-bearing mouse a total of 3 times for 2 days to prepare a study group. The size of tumor was measured every day, and the antitumor effect of the antibody #13 was observed. On the other hand, PBS(−) was administered instead of the antibody to the remaining 5 cancer-bearing mice, which were in turn used as a control group.

As a result of observing the antitumor effect, the tumor volumes of the B16F10-transplanted study group receiving the antibody #13 were increased to approximately 150%, 200%, 370%, and 630% at days 4, 6, 8, and 11, respectively, with the tumor volume at the start of antibody administration defined as 100%. On the other hand, the tumor volumes of the EMT-6-transplanted study group receiving the antibody #13 were reduced to 51% at day 4, approximately 31% at day 6, and 9% at day 8 with the tumor volume at the start of antibody administration defined as 100%, and their tumors were almost completely regressed by days 10 to 14. The tumor volumes of both of the B16F10-transplanted study group and the EMT-6-transplanted study group in the control group receiving PBS(−) were increased to approximately 230%, 290%, 470%, and 800% at days 4, 6, 8, and 11, respectively.

From the results mentioned above, the results of detection of CAPRIN-1 using the antibody #8 were not observed to correlate with cancer therapeutic effects based on the antitumor activity of the antibody, whereas the results of detection of CAPRIN-1 using the antibody #14 were observed to correlate with cancer therapeutic effects based on the antitumor activity of the antibody. Specifically, the results of detecting CAPRIN-1 using the antibody #14 exhibited score 3 for the EMT-6 transplant-derived cancer tissues, demonstrating CAPRIN-1 overexpression and pharmacological effects based on the antitumor activity of the administered antibody.

On the other hand, the results of detection of the expression of CAPRIN-1 using the antibody #14 exhibited score 1 for the B16F10 transplant-derived cancer tissues. Thus, the expression of CAPRIN-1 was not detected. In addition, the antibody #13 having antitumor activity did not produce pharmacological effects when administered to the cancer-bearing mice in which B16F10 were transplanted.

From these results, it can be predicted that a cancer or an individual determined as having a high expression level of CAPRIN-1 by detecting CAPRIN-1 in a cancer tissue using the antibody #14 of the present invention specifically binding to CAPRIN-1 can get high therapeutic effects by administering an anti-CAPRIN-1 antibody having antitumor effects.

INDUSTRIAL APPLICABILITY

The present invention is industrially useful for the diagnosis of cancers.

All publications, patents, and patent applications cited herein are incorporated herein by reference in their entirety.

FREE TEXT OF SEQUENCE LISTING

-   SEQ ID NOs: 31 to 36, and 38 to 42: Primer 

The invention claimed is:
 1. A method for detecting a cancer in an individual, comprising: detecting an expression level of CAPRIN-1 in a biological sample from the individual above that of a healthy subject through an antigen-antibody reaction comprising contacting the sample with a monoclonal antibody having a heavy chain variable region comprising the amino acid sequence shown in SEQ ID NO:70 and a light chain variable region comprising the amino acid sequence shown in SEQ ID NO:71, or an antigen-binding fragment thereof.
 2. The method according to claim 1, wherein CAPRIN-1 to be detected is (a) a polypeptide having the amino acid sequence shown in any even-numbered SEQ ID NO shown in SEQ ID NOs: 2 to 30 in the Sequence Listing, or (b) a polypeptide having 85% or higher sequence identity to the polypeptide.
 3. The method according to claim 1, wherein the biological sample is derived from a human, a dog, or a cat.
 4. The method according to claim 1, wherein the biological sample is derived from a dog, and CAPRIN-1 to be detected has an amino acid sequence shown in SEQ ID NO: 6, 8, 10, 12, or
 14. 5. The method according to claim 1, wherein the biological sample is derived from a human, and CAPRIN-1 to be detected has an amino acid sequence shown in SEQ ID NO: 2 or
 4. 6. The method according to claim 1, wherein the detection of the expression level of CAPRIN-1 is carried out using an immunological assay method.
 7. The method according to claim 6, wherein the immunological assay method is ELISA and/or an immunohistochemical staining method.
 8. The method according to claim 1, wherein the biological sample is a body fluid, a tissue, or a cell.
 9. The method according to claim 1, wherein the cancer is at least one cancer selected from the group consisting of breast cancer, brain tumor, esophagus cancer, stomach cancer, lung cancer, liver cancer, kidney cancer, thyroid gland cancer, spleen cancer, pancreas cancer, large bowel cancer, skin cancer, ovary cancer, uterus cancer, prostate cancer, bladder cancer, testis cancer, osteosarcoma, and fibrosarcoma.
 10. The method according to claim 2, wherein the biological sample is derived from a human, a dog, or a cat.
 11. The method according to claim 2, wherein the biological sample is derived from a dog, and CAPRIN-1 to be detected has an amino acid sequence shown in SEQ ID NO: 6, 8, 10, 12, or
 14. 12. The method according to claim 3, wherein the biological sample is derived from a dog, and CAPRIN-1 to be detected has an amino acid sequence shown in SEQ ID NO: 6, 8, 10, 12, or
 14. 13. The method according to claim 2, wherein the biological sample is derived from a human, and CAPRIN-1 to be detected has an amino acid sequence shown in SEQ ID NO: 2 or
 4. 14. The method according to claim 3, wherein the biological sample is derived from a human, and CAPRIN-1 to be detected has an amino acid sequence shown in SEQ ID NO: 2 or
 4. 15. A method for selecting an individual-specific therapeutic drug for a cancer, comprising: detecting an expression level of CAPRIN-1 in a biological sample from the individual comprising contacting the sample with a monoclonal antibody having a heavy chain variable region comprising the amino acid sequence shown in SEQ ID NO:70 and a light chain variable region comprising the amino acid sequence shown in SEQ ID NO:71, or an antigen-binding fragment thereof; and, when the expression level is statistically significantly higher than that of a healthy individual, selecting a CAPRIN-1-targeting drug as a therapeutic drug for the cancer suitable for administration to the individual from which the biological sample was derived.
 16. The method for selecting an individual-specific therapeutic drug for a cancer according to claim 15, wherein the CAPRIN-1-targeting drug is a monoclonal antibody having immunological reactivity with CAPRIN-1, or an antigen-binding fragment thereof.
 17. A method for detecting CAPRIN-1 in an individual, comprising: detecting CAPRIN-1 in a biological sample from the individual through an antigen-antibody reaction comprising contacting the sample with a monoclonal antibody having a heavy chain variable region comprising the amino acid sequence shown in SEQ ID NO:70 and a light chain variable region comprising the amino acid sequence shown in SEQ ID NO:71, or an antigen-binding fragment thereof. 